A steering column device is placed in a space for a driver's seat, between a meter panel provided above and a room for driver's knees provided below. The steering column device is equipped with a steering shaft, a steering wheel being mounted on the top end of the steering shaft and the lower end thereof being coupled to a vehicle body steering mechanism for controlling orientations of front wheels.
FIG. 1 shows a conventional steering column device 1. Generally, this steering column device 1 includes a tubular shaped column body 2 and a steering shaft 3 which penetrates inside the column body 2. The steering shaft 3 is rotatably supported by an upper bearing 31 and a lower bearing 32, which are respectively provided in proximity to both ends of the column body 2. A steering wheel, not illustrated, is coupled with one end thereof (in the right side in FIG. 1(A)), and the other end thereof (in the left side in FIG. 1(A)) is connected to a steering mechanism on the vehicle body side via an intermediate shaft.
The column body 2 is provided with an upper body mounting part 21 and a lower body mounting part 22, respectively on the two points along the longitudinal direction of the column body 2. The upper body mounting part 21 and the lower body mounting part 22 are respectively provided with a distance bracket 21d and a lower bracket 22t, each being U-shaped member having a flat bottom with a pair of feet 212 and a pair of feet 222, respectively, each of the pairs having feet parallel to each other and the tip ends of those feet being welded onto the column body 2.
On the vehicle body 9 side, a vehicle body side upper mounting part 91 and a vehicle body side lower mounting part 92 are fixed onto the positions corresponding to the distance bracket 21d and the lower bracket 22t respectively. The vehicle body side upper mounting part 91 and the vehicle body side lower mounting part 92 respectively have a pair of feet 912 and a pair of feet 922, each having an inner width into which an outer width of the distance bracket 21d and the lower bracket 22t are respectively placed suitably. The vehicle body side upper mounting part 91 is fixed onto the vehicle body 9 via an impact fracture member 913.
Each of the feet 912 of the vehicle body side upper mounting part 91 and the feet 212 of the distance bracket 21d are provided with mounting holes and a vehicle body side upper holding shaft member 911 penetrates into the mounting holes. The vehicle body side upper holding shaft member 911 is designed to hold the distance bracket 21d fitted between the feet 912 in tightened manner, by a cam member on which a column rock lever 93 is fixed and a cam member which is slidable along arc-shaped long holes 914 of the feet 912. The mounting holes provided on the feet 912 are arc-shaped long holes 914 made on an arc having as a center the vehicle body side lower holding shaft member 921 (described below) that servers as a tilt center. With this configuration, the column body 2 (that is, steering shaft 3 and steering wheel) can be tilted.
The feet 922 of the vehicle body lower mounting part 92 and the feet 222 of the lower bracket 22t are each provided with mounting holes and the vehicle body side lower holding shaft member 921 penetrates into the mounting holes. An ordinary bolt, a rivet pin or the like is employed as the vehicle body side lower holding shaft member 921. If it is a bolt, the member is fitted between the feet 922 by a bolt and nut being screwed together. If it is a rivet pin, the lower bracket 22t is rotatably supported by crimping the rivet pin, which penetrates into the feet 922 simultaneously with the lower bracket 22t fitted therebetween.
The mounting holes provided on the feet 922 of the vehicle body side lower mounting part 92 are open downwardly from the vehicle body (hereinafter, referred to as “lateral open hole 923”), and a shaft part of the vehicle body side upper holding shaft member 911 can escape therefrom. In the case of vehicle collision, if a driver comes into collision with the steering wheel due to abrupt speed reduction, thereby applying a downward force (left direction in FIG. 1) onto the steering shaft 3 and column body 2, the shaft part of the vehicle body side lower holding shaft member 921 escapes from the lateral open hole 923, and simultaneously the impact fracture member 913 is broken. Accordingly, a damage the driver may suffer will be reduced.
As described above, the conventional type steering column device 1 has been configured such that the distance bracket 21d and the lower bracket 22t are separately made in advance, and they are mounted on the column body by welding. Therefore, not only steps for making the distance bracket 21d and the lower bracket 22t are respectively required, as well as a welding step and the like for fixedly positioning these elements onto the column body, but also quality control for welding is a significant issue, and thus cost reduction has not been achieved as intended.
In addition, a tubular member is employed as it is to make the column body 2. If a need arises to improve undesirable operability such as vibrations propagating up to the steering wheel due to vibrations originating from the vehicle body, a technique for improving flexural rigidity and resistance to vibration property of the steering column is applied by making thicker the tubular member, as a material of the column body 2, or by reinforcing constitutional elements of the upper body mounting part 21 and the lower body mounting part 22. However, there is a problem that an increase in weight cannot be avoided.
Furthermore, in some vehicles, due to a vibration property, a vibration level which is acceptable by the steering column device is different between in the vertical direction with respect to the vehicle traveling direction (vibrations such as shaking the wheel up and down when viewed from the driver, referred to as “vertical direction” here), and in horizontal direction (vibrations such as shaking the wheel from side to side), and there may be a case that a heavily high rigidity is required in the vertical direction, rather than the horizontal direction.
If a tubular member is employed as it is for the column device like conventional manner, it is substantially difficult to vary the flexural rigidity and directionality in vibration level. Therefore, a possible countermeasure is only to make the wall thicker, thereby rendering the flexural rigidity and vibration property in horizontal direction also unnecessarily enhanced, even if it is not a significant requirement. It is needless to say that in the case above, the weight is increased and thus reversing the trend.
Furthermore, there is a type of steering column device which has a steering lock unit being mounted on the upper part thereof, and in this type of steering column device, natural vibration frequency of the column body is relatively reduced due to the mass of the steering lock unit. Accordingly, the natural vibration frequency of the steering column device approaches to the vibration frequency of the vehicle body, and resonance may be easily established. Therefore, the above problem becomes further critical.